The Diversity of Species

1. The Diversity of Species

2. Speciation • A single species can diverge to produce several new species • Ancestral South American tortoise split to produce the giant Galapagos Island tortoise • Speciation is a key par of the theory of evolution

3. Speciation • 3 broad processes that work together: • Natural selection - better adapted to environment. • Population changes over time as genes accumulate small changes in response to natural selection - microevolution • Accumulation of so many changes – new species formation and multiplication of species • Rapid series of speciation can lead to development of whole new collection of species, genera, families or higher classification groups - macroevolution

4. Extinction • Another important process in evolution that helps us to identify current species via the fossil record • Vast disappearance of species over time allows new species to evolve

5. The Biological Species Concept • The biological species model defines a species as a reproductively isolated group of organisms. • These organisms can be identified through consistent differences in morphological and physiological traits as well as genetic differences

6. Mechanisms of Speciation • Isolating mechanisms • Pre-reproductive isolating mechanisms • Post reproductive isolating mechanisms • Allopatric speciation • Sympatric speciation • Separation of groups, preventing them from producing fertile, viable offspring • Can occur before or after reproduction • After isolation, different phenotypes can occur

7. Pre-reproductive isolating mechanisms

8. Pre-reproductive isolating mechanisms • Summarise the following types of isolating mechanisms: • Geographic • Temporal (time) • Behavioural • Morphological

9. Post-reproductive isolating mechanisms • two frogs from different species will be unable to mate and produce fertile offspring • Chromosomes in gametes do not line up successfully at meiosis, so no zygotes formed • This is an example of post-reproductive isolation. Reproduction can occur, however no viable offspring produced

10. Post-reproductive isolating mechanisms • Summarise the three types of post-reproductive isolating mechanisms • Explain why hybrid sterility is not a barrier in plants as it is in animals.

12. Allopatric Speciation • Allopatric speciation is when new species arise due to isolation of a population by geographical barriers. • Features such as rivers or mountain ranges isolate populations of animals and plants. • Movement of land-masses by continental drift led to geographical isolation millions of years ago.

14. Sympatric Speciation • Sympatric speciation is when new species arise despite occupying the same geographical area. • Ecological barriers - although groups are not geographically isolated from each other they may be isolated by occupying different habitats or breeding areas, pH and salinity. • Behavioural barriers – a population may carry out complex mating rituals that may create a barrier to reproduction. • Different timings, locations or mating dances may result in members of a population, who are not geographically separated, not being able to mate with each other. .

16. Questions • Complete questions on page 200 of your textbook. • Make sure that you answer questions thoroughly and make notes on anything that you’re not sure about.

17. Useful slides • The following slides are from another source – I have added them in for some extra notes if you want to read them.

18. Isolating Mechanisms • Since members of the same species share a common gene pool, in order for a species to evolve into 2 new species, the gene pools must be separated into 2 • As new species evolve, populations become reproductively isolated from each other

19. Reproductive isolation • When the members of 2 populations cannot interbreed and produce fertile offspring

20. Behavioral Isolation • When two populations are capable of interbreeding but have differences in courtship rituals or other reproductive strategies

21. Eastern & Western Meadowlark

22. Geographical Isolation • When two populations are separated by geographic barriers such as rivers, mountains, or bodies of water

23. Albert & Kaibab Squirrels

24. Temporal Isolation • When 2 or more species reproduce at different times Rana aurora - breeds January - March Rana boylii - breeds late March - May

25. Testing Natural Selection in Nature Q: Can evolution be observed in nature? A: YES

26. The Grants

27. Testing Natural Selection in Nature • Darwin hypothesized that finches had descended from a common ancestor and overtime, natural selection shaped the beaks of different bird populations as they adapted to eat different foods • The Grants, realized that Darwin’s hypothesis relied on two testable assumptions

28. There must be enough heritable variation in these traits to provide raw materials for natural selection • Differences in beak size and shape must produce differences in fitness that cause natural selection to occur

29. Variation • The Grants identified and measured every variable characteristic of the birds on the island • Their data indicated that there is a great variation of heritable traits among the Galapagos finches

30. Natural Selection • During the… • Rainy season – enough food for everyone, no competition • Dry season – some foods become scarce • At that time, differences in beak sizes can mean the difference between life and death • Birds become feeding specialists

31. Natural Selection • The Grants discovered that individual birds with different size beaks had different chances of survival during a drought

32. Speciation in Darwin’s Finches • Speciation in the Galapagos finches occurred by founding of a new population, geographical isolation, changes in the new population’s gene pool, reproductive isolation and ecological competition

33. Founders Arrive • Many years ago, a few finches from South American mainland • Species A, flew or were blown to one of the Galapagos Islands

34. Geographic Isolation • Later on, some birds from species A crossed to another island in the Galapagos group • The finches then became unable to fly from island to island and become isolated from each other and no longer share a common gene pool

35. Changes in the Gene Pool • Overtime, populations on each island became adapted to their local environments

36. Reproductive Isolation • Now imagine that a few birds from the second island cross back to the first island • Q: Will the population A birds, breed with the population B birds? • A: Probably not

37. Ecological Competition • As these two new species live together in the same environment, they compete with each other for available seeds • The more different birds are, the higher fitness they have, due to less compitition

38. Continued Evolution • This process of isolation on different islands, genetic change, and reproductive isolation probably repeated itself time and time again across the entire Galapagos island chain • Over many generations, it produced the 13 different finch species found there today

39. Studying Evolution Since Darwin • It is useful to review and critique the strength and weakness of evolutionary theory • Darwin made bold assumptions about heritable variation, the age of the Earth, and the relationships among organisms • New data from genetics, physics, and biochemistry could have proved him wrong on many counts, and they did not • Scientific evidence supports the theory that living species descended with modification from common ancestors that lived in the past

40. Limitations of Research • The Grants data shows how competition and climate change affects natural selection • However, they did not observe the formation of a new species

41. Unanswered Questions • Many new discoveries have led to new hypotheses that refine and expand Darwin’s original ideas • No scientist suggests that all evolutionary processes are fully understood. Many unanswered questions remain

42. Why Understanding Evolution is Important? • Evolution continues today Ex.) • Drug resistance in bacteria and viruses • Pesticide resistance in insects • Evolutionary theory helps us understand and respond to these changes in ways that improve human life